class Solution:
    def countDigitOne(self, n: int) -> int:
        low, cur, high = 0, n % 10, n // 10
        digit, res = 1, 0
        while high != 0 or cur != 0:
            if cur == 0:
                res += high * digit
            elif cur == 1:
                res += high * digit + low + 1
            else:
                res += (high + 1) * digit
            low += cur * digit
            cur = high % 10
            high //= 10
            digit *= 10
        return res